About the RNG and Realizable turbulence models

Freeman

Hi all!

I've got aquestion that in fluent users guide I'm not able to resolve. I've read that the RNG model comes from the application of the Renormalization Group Method (RG) to the instantaneous Navier-Stokes equations, so I think this RG method is another different way to get an averaged Navier-Stokes equations as it is done with the application of the Favre average to get the standard k-e model: is this correct? I mean, has the RG method applied to the RNG model nothing to do with the "RANS method" or I am confused?

Another thing, is the Realizable model also derived from the application of the RG method or it is another Favre average derivedmodel?

By the way, could any of you explain me a bit what is the idea of the RG method? I've found many hits in google about this theory, but they are VERY advanced to me; for now I'm only interested in the idea and how this method affects the instantaneous Navier Stokes equations and what are the differences about applying this method or the classical Favre average.

Thanks to all!